Koni sport shocks and shorter springs?

[The Glademister]

So I'm looking at getting some 250lb. Weltmeister autocross front springs for my '88 924S which should really help on the front end dipping during braking. These springs though also lower by 1.5". How does that impact the Koni sport shock inserts I've already installed? If the spring is lowering the strut mount by 1.5" isn't that effectively compressing the shock the same amount? Would that shorten the life of the shock?

[Makis]

I would not think so. As long as you are not riding on the bump stops most of the time you should be fine. Good quality springs matched to the car weight should not do this.

[flash968]

shortening the stroke, and increasing spring rate, could theoretically shorten the life of the strut seal, as the friction could be increased, but i doubt that a relatively soft spring like a 250 will make all that much difference

i would be more concerned with the geometrical change of a 1.5" drop - that puts a LOT of load on the ball joints, and other suspension bushings - do not add big wheels if you do that, and definitely watch the weight on them, unless you plan to upgrade bushings and ball joints

also, if your front end is dipping under braking, you could try changing the proportion of front to rear braking, and add more rear - many of these cars are biased to the front for safety, but that leaves a lot of rear brake capability on the table

[The Glademister]

Originally Posted by flash968

shortening the stroke, and increasing spring rate, could theoretically shorten the life of the strut seal, as the friction could be increased, but i doubt that a relatively soft spring like a 250 will make all that much difference

i would be more concerned with the geometrical change of a 1.5" drop - that puts a LOT of load on the ball joints, and other suspension bushings - do not add big wheels if you do that, and definitely watch the weight on them, unless you plan to upgrade bushings and ball joints

Thanks for the heads up on that. Part of my plan is to have a race alignment done by a local expert after installing the springs. He should be able to detect overloaded or weak components. As for wheel size, I'm running stock 15" phone dials so that should help.

Originally Posted by flash968

also, if your front end is dipping under braking, you could try changing the proportion of front to rear braking, and add more rear - many of these cars are biased to the front for safety, but that leaves a lot of rear brake capability on the table

Someone was asking me about bias the other day. How are brake bias changes made on these cars?

[petrolhead611]

By lowering the front end relative to the rear, you are automatically biasing the braking more to the front. Why not check that the car has same front/rear ride heights prior to changing springs. Just measure rockerpanel-ground at front of rear wheel arch and back of front wheel arch; they should be the same

[The Glademister]

Already done that Petrol. I lowered the rear using the eccentric bolts. 944s and 924Ss were shipped to the U.S. with the rear end raised to meet federal safety rules on bumper height. After dropping the rear the car is level front to back.

[Makis]

The rear spring rate will be too soft when you put the 250 springs at the front. You will be able to notice this when you go fast and feel the rear has got lots more suspension travel then the front.

[The Glademister]

Originally Posted by Makis

The rear spring rate will be too soft when you put the 250 springs at the front. You will be able to notice this when you go fast and feel the rear has got lots more suspension travel then the front.

Something to keep in mind for sure. There's excellent information on the Clark's Garage site on all this under SUSP-15. This car does exhibit oversteer with the current suspension, alignment and tires. Some of that can be corrected with tire pressure adjustments but once I commit to a spring change, the alignment that follows will be something I'm stuck with for awhile. Can't really afford to get the car re-aligned every other week.

[Dave L]

I have konis and Weltmiester 250 springs. I also have the CS900 spacers so its stock hieght. THe car doesnt much dive while braking but it does understeer, by dropping the front you will also put more weight on the front and make the understeer worse. I have reduced the understeer somewhat by upgrading from the 18mm to the 19mm rear sway bar. Although this has helped the only proper solution is to upgrade the rear torsion bars to match the front springs.

If I had to do it again I would probably get the 200lb springs so its closer in rate to the torsion bars and still keep it at the stock height. I would also do the 968 M030 sway bars front and rear.

[The Glademister]

Originally Posted by Dave L

I have konis and Weltmiester 250 springs. I also have the CS900 spacers so its stock hieght. THe car doesnt much dive while braking but it does understeer, by dropping the front you will also put more weight on the front and make the understeer worse. I have reduced the understeer somewhat by upgrading from the 18mm to the 19mm rear sway bar. Although this has helped the only proper solution is to upgrade the rear torsion bars to match the front springs.

If I had to do it again I would probably get the 200lb springs so its closer in rate to the torsion bars and still keep it at the stock height. I would also do the 968 M030 sway bars front and rear.

Thanks Dave, that's exactly the info I'm seeking and it does confirm what I thought might happen. Changing the torsion bars is a major operation from what I've read so far. Also, I think I read in the SCCA rules that spring spacers are not allowed in Street Prepared class which is where I want to be.

(Correction - rules do state that "Spacers are allowed above or below the spring")

My current thought is to change to stock height 200 lb. springs and get the race alignment with camber set. I'm going to stick with stock sway bars and get a feel for that set-up. If body roll is a problem at that point I can go to heavier sway bars and not effect alignment.

[petrolhead611]

Hi, if you really do have slight oversteer, don't mess with it. Drive the car on the torque curve for AutoX, its exactly what is needed. I have added a rear sway bar,and messed with my tyre pressures and brands to try to induce oversteer from a normally understeering car to achieve this very thing. You can now turn in late, trail brake on second & third gear corners, and steer out of the corners on the throttle(provided you can maintain traction) and a bit of opposite lock. The brakes are still biased towards the front, but sometimes unsettling the rear just before a sharp bend is just what is needed.

[The Glademister]

I think I would describe it as a bit more than slight oversteer. Some of that induced by lifting throttle in turns. I'm confident I'm on a good course of action with the modifications. The main point being that if I'm going to change springs, now is the time to do it. Before getting the race alignment and our club's test & tune event in March. If I've seriously screwed the suspension up at that point at least I'll have a couple of weeks to go back to the current set-up.

[petrolhead611]

Ah, what you describe is lift-off oversteer, not so easy to cure, but very handy to induce the tail out in the really tight bends that we have in AutoX in the UK because of the limitation of a max 200yard by 200 yard area in which the track must reside.

[petrolhead611]

Forgot to mention, we even use the parking brake on some of the tightest turns.

[vtach]

just in case anyone needs -- i have a set of hypercoil springs for sale 200lbs
$80 bucks for the pair 6 months new !
thanks
v-tach